1. Field of the Invention
The present invention relates to a fuel supply pump for an internal combustion engine (hereinafter referred to as an engine).
2. Description of the Related Art
An accumulator fuel injection system as shown in FIG. 4 is conventionally used as a diesel engine fuel injection system. The accumulator fuel injection system includes an accumulator (common rail) 100, in which a high-pressure fuel, supplied under pressure by a fuel supply pump 101, is accumulated. The high-pressure fuel in the common rail 100 is injected into each cylinder of the diesel engine through a fuel injection valve (injector) 102.
A fuel supply pump 101 includes a low-pressure supply pump 103, pump elements, such as a plunger 104, a plunger drive means, etc. The fuel in a fuel tank 105 is pumped by the low-pressure supply pump 103 and is supplied to a pressure chamber 106. The fuel supplied to the pressure chamber 106 is increased to high pressure by the reciprocating motion of the plunger 104 and is supplied to the common rail 100 under pressure. The reciprocating motion of the plunger 104 is activated by the plunger drive means.
The plunger drive means includes a drive shaft (cam shaft) 107 connected to an engine crankshaft and rotatively driven by the engine, a cam 108 assembled eccentrically on the cam shaft 107, a cam ring 109 driven by the cam 108 through a metal bushing (not shown) and revolved (orbited) about the center of the cam shaft 107, etc. A sliding surface 110 of the cam ring 109 is kept in pressure contact with a sliding surface 112 of the plunger 104 by an urging means 111. The plunger 104 is reciprocated by the orbiting of the cam ring 109 and the pressure of the urging means 111. In the process, the sliding surface 112 of the plunger 104 slides over the sliding surface 110 of the cam ring 109.
By the rotation of the cam shaft 107, the low-pressure supply pump 103 sucks in the low-pressure fuel from the fuel tank 105 and discharges it to the pressure chamber 106.
In order to maintain the lubricity of a sliding portion between the plunger 104 and the cam ring 109, the low-pressure fuel discharged from the low-pressure supply pump 103 is supplied to the sliding portion. Also, the lubricity of a sliding portion in the plunger drive means, such as a sliding portion between a metal bushing and the cam 108, is improved (for example, Japanese Unexamined Patent Publication No. 2002-310039).
In a bearing portion of the cam shaft 107 or, especially, a portion adjacent to the low-pressure supply pump 103, on the other hand, the lubricity between a metal bushing 113 and the cam shaft 107 is maintained by the low-pressure fuel leaking from the low-pressure supply pump 103. The low-pressure fuel oil supplied by leakage, however, varies in flow rate thereof such that the lubricating conditions are liable to vary.